Multilayer Hollow Microspheres Research Articles

Tailoring the morphology through alkali treatment: dynamics of pattern formation

ABSTRACTDiversified technological applications necessitate the tailoring of morphology of materials at nanoscale. This paper reports morphological modifications of boron carbide (BC) at nanoscale through alkali (NaOH) treatment. The multilayered hollow microspheres of BC, obtained by the refluxion of castor oil with boric acid, are subjected to exfoliation by sonicating it in the ethanol–water mixture. The attractive morphologies evolved in the sonication process as a result of changing the BC concentration, auxiliary agent and sonication time are analysed. The multilayered hollow structure on sonication with NaOH yields flower-like morphology that seems to evolve from the basic spindle structure. The morphological tuning makes the study relevant in the areas like bleaching, where the surface area is crucial.

Low temperature synthesis of multilayered-hollow microspheres of boron carbide from castor oil for photonic applications

The development of boron carbide microspheres of various types is of greater interest because of their applications in thermal insulation, imaging, luminescent coating, and drug delivery. The present methods of synthesis involve costlier equipment, toxic chemicals, and high temperature. This work describes low temperature, green synthesis of multilayered-hollow microspheres of boron carbide using the natural carbon precursor—castor oil. Refluxion of boric acid with castor oil and successive cooling results in the formation of boron carbide and is subjected to thermal deposition at 300 °C for 1 h to get a thin film. The field emission scanning electron microscopic analysis shows the formation of multilayered hollow microspheres in the film whose surface morphology is studied using an atomic force microscope. The X-ray diffraction, X-ray mapping, and energy dispersive spectroscopic and Fourier transform infrared spectroscopic analyses confirm the formation of boron carbide which is thermally stable and gives a yield of 37% at 800 °C. The optical characterization of the sample is carried out with ultraviolet-visible and photoluminescence spectroscopic techniques. The chromaticity diagram and the power spectrum suggest the possible use of the material as a blue light emitter.

Detection of Dopamine Using Chemically Synthesized Multilayered Hollow Microspheres

Microspheres made of alternating layers of two different conducting polymers, poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole), have been found to be sensitive to dopamine (DA) oxidation, presenting a very well-defined and linear response in the range of DA concentrations from 0.5 to 2 mM. The novelty of the present study is the use of doped multilayered hollow microspheres, which are prepared by successive oxidative chemical polymerizations in FeCl3 aqueous solution. The multilayered microspheres were characterized by FTIR and UV-visible spectroscopies, scanning and transmission electron microscopies, and atomic force microscopy. The UV-visible bands confirm that the multilayered system is not well doped with FeCl4(-) counterions. Therefore, the doping level was increased by further oxidation with LiClO4 before DA electrochemical detection. Despite that the range of concentration detection was limited from 0.5 mM to 2 mM, doped hollow multilayered microspheres show a very good anodic peak current response compared to single-layer films fabricated with an individual conducting polymer and activated by gold nanoparticles.

Polyaniline/carbon nanotube multi-layered hollow microspheres with sandwich structure and their electrochemical performance

Novel composite hollow microspheres with the unique “sandwich” structure were prepared by alternate coverage of polyaniline (PANI) and carboxyl-functionalized multi-walled carbon nanotubes (f-MWNTs) on the surface of spherical templates, formed by in situ polymerization. It was proved that the incorporation of f-MWNTs into the PANI layers could strengthen the stability of hollow microspheres, which had been demonstrated by other researchers in the preparation of carbon nanotubes-based hollow microcapsules. Specially, Raman spectra revealed that the driving force for adsorbing f-MWNTs was not electrostatic interaction, but hydrogen bond and additional π–π conjugated interaction. With the measurements of conductivity and electrochemical performance, it was also proved that the facile strategy to introduce f-MWNTs into the shells could effectively improve conductivity and electrochemical performance of PANI hollow microspheres.

Chitosan/Functionalized Multiwalled Carbon Nanotubes Multilayer Hollow Microspheres Prepared via Layer-by-Layer Assembly Technique

Novel multilayer hollow microspheres were fabricated via the layer-by-layer (LBL) assembly technique by the electrostatic interaction between the polycation chitosan (CHI) and the anion carboxyl-functionalized multiwalled carbon nanotubes (f-MWNTs) on sacrificial polystyrene sulfonate (PSS) microsphere templates. The successful stepwise growth of the CHI/f-MWNTs multilayers in different pH media was compared by zeta potential measurement and scanning electron microscopy (SEM) analysis. The morphologies of the hollow microspheres were characterized by transmission electron microscopy (TEM) and SEM. The swelling and collapse of the hollow microspheres occurred during the template removal by dissolution and the drying process. It was found that more f-MWNTs had been deposited onto the surface of the PSS microspheres at pH 3 than at pH 5, confirmed by SEM and thermogravimetric analysis (TGA). Furthermore, this result is consistent with the differences of the electrical conductivities of the hollow microspheres obtained from the different pH media. It is also found that in the etching process, the different etching reagents, such as DMF and toluene, obviously affected the electrical conductivity of the final hollow microspheres.

Thermomechanical processes of composite materials under the action of intense energy fluxes

We propose mathematical models for determining the parameters of mechanical action under volumetric absorption of intense energy fluxes acting on targets consisting of heterogeneous materials. We focus on spheroplastics—materials having in their composition multilayer hollow microspheres.